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Date:   Thu, 16 Jul 2020 21:03:01 -0400
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     NeilBrown <neilb@suse.de>
Cc:     Jeff Layton <jlayton@kernel.org>, linux-nfs@vger.kernel.org
Subject: Re: nfs4_show_superblock considered harmful :-)
Message-ID: <20200717010301.GC18568@fieldses.org>
References: <871rn38suc.fsf@notabene.neil.brown.name>
 <20200529220608.GA22758@fieldses.org>
 <87a71n7dek.fsf@notabene.neil.brown.name>
 <20200715185456.GE15543@fieldses.org>
 <20200716171958.GB18568@fieldses.org>
 <87tuy7vxeb.fsf@notabene.neil.brown.name>
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On Fri, Jul 17, 2020 at 09:43:40AM +1000, NeilBrown wrote:
> On Thu, Jul 16 2020, J. Bruce Fields wrote:
> > --- a/fs/nfsd/nfs4state.c
> > +++ b/fs/nfsd/nfs4state.c
> > @@ -507,6 +507,16 @@ find_any_file(struct nfs4_file *f)
> >  	return ret;
> >  }
> >  
> > +static struct nfsd_file *find_deleg_file(struct nfs4_file *f)
> > +{
> > +	struct nfsd_file *ret;
> > +
> > +	spin_lock(&f->fi_lock);
> > +	ret = nfsd_file_get(f->fi_deleg_file);
> 
> A test on f->fi_deleg_file being non-NULL would make this look safer.
> It would  also make the subsequent test on the return value appear sane.

Yes, thanks!-b.

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index c2a2e56c896d..6e8811e7c134 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -509,10 +509,11 @@ find_any_file(struct nfs4_file *f)
 
 static struct nfsd_file *find_deleg_file(struct nfs4_file *f)
 {
-	struct nfsd_file *ret;
+	struct nfsd_file *ret = NULL;
 
 	spin_lock(&f->fi_lock);
-	ret = nfsd_file_get(f->fi_deleg_file);
+	if (f->fi_deleg_file)
+		ret = nfsd_file_get(f->fi_deleg_file);
 	spin_unlock(&f->fi_lock);
 	return ret;
 }